A variety of propeller based lift platforms have been designed over the years which use two or more propellers coupled to a single engine. Typically the propellers are ducted, thus increasing propeller efficiency, decreasing noise and eliminating the dangers associated with exposed blades.
In general, ducted propeller platforms do not possess autorotation capabilities. In order to achieve at least a level of fail-safe operation, such platforms often employ redundant engines thus allowing the platform to overcome the failure of a single engine. Unfortunately as such an approach does not provide complete system redundancy, the failure of any of a variety of other components within the drive system will still lead to the catastrophic failure of the platform.
A typical ducted platform uses fixed-pitch propellers, thus simplifying the overall design. As a result, however, such a platform must use an internal combustion engine since turbine engines, although more efficient, suffer from spin-up lag. Although the inherent lag in turbines can be overcome using variable-pitch propellers, this defeats the mechanical simplicity and the weight savings offered by the used of fixed-pitch propellers.
Another issue confronting ducted propellers is their susceptibility to upsets due to sudden wind gusts.
Although a variety of fixed-pitch propeller platforms have been designed, these platforms typically require the use of internal combustion engines, provide limited fail-safe operation, and are susceptible to wind gusts. The present invention overcomes these limitations.